(a) Technical Field
The present disclosure relates to an optical mask for forming a pattern, and more particularly, to an optical mask including a halftone layer.
(b) Description of the Related Art
The ability to form fine patterns in the manufacture of electronic devices (such as display devices) is of interest to the electronics industry. For example, forming fine patterns in a display device allows the linewidth of wiring, electrodes, or other interconnects in the display device to be reduced. This can then result in form factor reduction and/or increased resolution of the display device.
In general, a photolithography process is used to form a pattern of wiring, electrodes, or other interconnects in an electronic device. The photolithography process generally includes forming a first layer (that is to be etched or patterned, e.g., a wiring/electrode layer) on a substrate, forming a photoresist layer (e.g., a photosensitive layer) on the first layer, positioning a mask (e.g., an optical mask) above the photoresist layer, and exposing the photoresist layer through the mask using a light source (in a light exposure system). The mask typically includes a light transmitting portion (that allows light to be transmitted through the mask) and a light blocking portion (that prevents light from transmitting through the mask). A mask consisting of a light blocking portion and a light transmitting portion is called a binary mask.
After the photoresist layer has been exposed using the light source, a photosensitive pattern is formed by developing the exposed photoresist layer. Next, the first layer is etched using the photosensitive pattern as an etching mask, so as to form a desired pattern of electrodes, wiring, or other interconnects.
As previously stated, it is desirable to reduce the linewidth of a pattern of wiring, electrodes, or interconnects in a display device, so as to reduce the form factor and/or increase the resolution of the display device. However, reductions in linewidth of the pattern may be limited by the resolution of the light exposure system. For example, the smallest feature size or linewidth that can be formed (or resolved) typically depends on a wavelength of the light source. To overcome the inherent resolution limitations in existing light exposure systems, various improvements have been proposed (e.g., relating to new exposure systems, lithography processes, or optical imaging materials).
Although the resolution of a light exposure system may be improved using one or more of the above proposed means, other challenges may arise. For example, in forming a fine pitch wiring pattern, a fine-patterned mask (e.g., a fine-patterned binary mask) is usually required. However, the decreased linewidth/spacing on the fine-patterned mask may result in a reduction in exposure sensitivity. This is because less light can pass through the light transmitting portion of the fine-patterned mask, compared to a mask with a larger linewidth/spacing pattern. As a result of the reduced exposure sensitivity, portions of the photoresist layer on the substrate may not be fully exposed and developed during the photolithography process. This may subsequently impact the quality of the photosensitive pattern and formation of the fine wiring pattern.